Fluid compressor and fuel cell vehicle

ABSTRACT

An air compressor as a fluid compressor includes: a suction port and a delivery port provided at upper and lower portions, respectively, of a pump chamber; a suction passage in communication with the inside of the pump chamber via the suction port; a delivery passage in communication with the inside of the pump chamber via the delivery port ( 88 ); and a driving rotor and a driven rotor provided in the pump chamber. At least a part of the suction passage is located below the suction port.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a fluid compressor that includes: anupper port and a lower port that are located at upper and lowerportions, respectively, of a pump chamber; an upper passage incommunication with the inside of the pump chamber via the upper port;and a lower passage in communication with the inside of the pump chambervia the lower port; and a rotor disposed in the pump chamber, and a fuelcell vehicle that is equipped with the fluid compressor.

2. Description of Related Art

A fuel cell system is contemplated that has a fuel cell stack thatgenerates electric power through an electrochemical reaction betweenfuel gas, such as a gas containing hydrogen, and oxidation gas, such asair. The fuel cell stack is constituted by stacking a plurality of fuelcell sets, each of which has a membrane-electrode assembly (MEA) that isconstituted of an anode, an electrolyte membrane, and a cathode; andseparators, for example. That is, each unit fuel-cell cell isconstituted by placing an anode and a cathode, respectively, on oppositesides of an electrolyte membrane that is constituted of a polymerion-exchange membrane. The MEA is then placed between two separators. Afuel cell stack that generates a high voltage is constituted by stackinga plurality of individual unit fuel cells and sandwiching the stackbetween current collecting plates, insulating plates, and end plates.

In such a fuel cell, fuel gas is supplied to the anodes and oxidationgas is supplied to the cathodes. Then, the fuel gas and oxidation gasundergo an electrochemical reaction to generate electricity.

For example, a vehicle may be equipped with the above described fuelcell system to supply electric power generated by the fuel cell to adriving motor that drives wheels. In this case, the fuel cell is used asan electric power source for the driving motor.

In a fuel cell system, a fluid compressor, such as an air compressor, isused to supply oxidation gas to the fuel cell. Hydrogen off-gas, i.e.,hydrogen gas that is discharged from the fuel cell and containsunreacted hydrogen gas, may also be mixed with fresh hydrogen gas in acirculation passage. The mixed hydrogen gas is to be supplied to thefuel cell to improve fuel efficiency. In this case, the fluid compressoris a hydrogen pump, and the hydrogen pump is provided in the circulationpassage.

Japanese Patent Application Publication No. 2005-180421(JP-A-2005-180421) describes a hydrogen compressor that has a pumpchamber defined by the inner surface of a pump housing and the innersurface of a bearing block; and two dual-lobe rotors disposed in thepump chamber. A delivery port is formed at the center of the bottom ofthe pump chamber, and a guide surface is formed in an inverted circulartruncated cone shape that slopes downward toward the opening edge of thedelivery port. One benefit of the described hydrogen compressor is thatwater that has been drawn into or condensed in the pump chamber flowsout through the delivery port and does not remain on the bottom of thepump chamber.

If a fluid compressor such as the hydrogen pump or air compressor isleft in an environment with a temperature below zero, water retained ingaps between the two rotors or between the rotors and the housing mayfreeze. In this case, the adherence of ice may make a smooth restart ofthe fluid compressor difficult or even impossible. Also, if ice isformed in recesses of the rotors, the ice may be caught between therotors when the fluid compressor is restarted and make a smooth start offluid compressor difficult. In addition, there is room for improvementin terms of minimizing of damage to the rotors.

Generally, a fuel cell system has a oxidation gas flow path to supplyair to the fuel cell and to discharge air off-gas, i.e., the air afterthe reaction, from the fuel cell. When water vapor contained in the aircondenses in the oxidation gas flow path, the water may flow from theupstream side or flow (back) from the downstream side into the aircompressor, which is located upstream of the oxidation gas flow path.Then, if the air compressor is left in a low-temperature environment,ice may form in the pump chamber of the air compressor. In the case of afuel cell vehicle equipped with a fuel cell system, due to thetemperature difference that generally occurs between the inside andoutside of the chamber, water tends to condense as described above.Further, water or snow thrown up when the fuel cell vehicle runs in therain or on the snow may be drawn in by the air compressor, and freezewithin the compressor.

In view of the above, a way to prevent entry of an excessive amountwater into a fluid compressor is desirable. In contrast, with thehydrogen compressor described in JP-A-2005-180421, ensuring that thewater present in the pump chamber flows smoothly toward the deliveryport is taken into account, but preventing the entry of water into thepump chamber is not taken into account. It is also contemplated toincrease the output of the motor that drives the rotors or to carry outa scavenging operation to direct a fluid such as air therethrough bydriving the fluid compressor at a relatively high rotational speed for acertain period of time after the fuel cell system is shut down, in orderto make a restart of the fluid compressor possible even if ice hasformed therein and to discharge the water in the fluid compressor. Sucha structure, however, may waste energy.

SUMMARY OF THE INVENTION

The present invention prevents the entry of an excessive amount of waterinto a fluid compressor of fuel cell vehicle.

A first aspect of the present invention relates to a fluid compressor,that includes: a pump chamber; an upper port that is provided at anupper portion of the pump chamber; an upper passage in communicationwith the inside of the pump chamber via the upper port; a lower portthat is provided at a lower portion of the pump chamber; a lower passagein communication with the inside of the pump chamber via the lower port;and a rotor that is provided in the pump chamber and rotates to compressa fluid introduced into the pump chamber through one of the upper portand the lower port and to discharge the compressed fluid through theother of the upper port and the lower port, in which at least a portionof the upper passage is located below the upper port.

According to the fluid compressor, because at least a part of the upperpassage in communication with the inside of the pump chamber via theupper port is located below the upper port, even if condensate water hasaccumulated on the wall surface of the upper passage, the water may beeasily discharged to the outside and the entry of an excessive amount ofwater into the pump chamber from the upper port side may be prevented.Therefore, formation of ice from water that has entered the pump chamberand malfunctions caused by the formation of ice in the pump chamber,such as inability to restart the air compressor smoothly, are lesslikely to occur.

The pump chamber may be defined within the housing. The upper port andthe lower port may be formed through a wall portion of the housing. Anupper connection member, to which a pipe is may be connected, may besecured to an upper portion of the housing and the upper passage isdefined within the upper connection member. A lower connection member,to which another pipe may be connected, may be secured to a lowerportion of the housing and the lower passage is defined within the lowerconnection member.

According to the fluid compressor described above, in a configuration inwhich the housing and both the upper and lower connection members areseparate components, malfunctions caused by the formation of ice in thepump chamber are less likely to occur.

The upper passage may have a lower edge, which is inclined or curvedgradually downward from the upper port side to the pipe connecting endside of the upper passage.

According to the fluid compressor described above, water that hasaccumulated on the wall surface of the upper passage is easilydischarged to the outside.

At least a portion of the upper passage side end of the upper port maybe located below the pump chamber side end of the upper port.

According to the fluid compressor described above, water that hasaccumulated on the wall surface of the upper port is easily dischargedto the outside.

At least a portion of the lower passage may be located below the lowerport.

According to the fluid compressor described above, even if water hasaccumulated on the wall surface of the lower passage, the water may bedischarged to the outside easily and entry of an excessive amount ofwater into the pump chamber from the lower port side may be prevented.For example, even if the lower passage is on the delivery side, waterthat has been discharged from the pump chamber is prevented from flowingback into the pump chamber. Therefore, malfunctions caused by theformation of ice in the pump chamber are much less likely to occur.

The lower port may include a portion that coincides with the lowermostend of the inner surface of the pump chamber, and may extend downwardfrom a bottom surface of the pump chamber or a side wall surface thatincludes the lowest end.

According to the fluid compressor described above, even if water hasentered or condensed in the pump chamber, the water is discharged easilyand prevented from remaining in the pump chamber and failures caused byformation of ice in the pump chamber 66 are much less likely to occur.

The upper passage may serve as a suction passage that directs a fluidinto the pump chamber through the upper port, and the lower passage mayserves as a delivery passage that delivers a fluid from the pump chamberthrough the lower port.

The lower passage may serve as a suction passage that directs a fluidinto the pump chamber through the lower port, and the upper passage mayserves as a delivery passage that delivers a fluid from the pump chamberthrough the upper port.

The rotor may have a spiral ridge. For example, the rotor may be atwisted roots rotor that has a plurality of lobes which are twistedspirally with respect to the axial direction or a screw rotor that has athread-like ridge.

According to the fluid compressor described above, even when water ispresent on the rotor, the water easily flows down along the ridge, whichmakes water less likely to stay on the rotor after the air compressor isstopped.

The fluid compressor may be used to compress a reactant gas for a fuelcell, which generates electric power through a reaction of the reactantgas.

According to the fluid compressor described above, because water isgenerated during the reaction of the reactant gas, advantage can beobtained due to a structure that at least a portion of the upperpassage, which is in communication with the inside of the pump chambervia the upper port, is located below the upper port.

The fluid compressor may be used as an air compressor, which compressesoxidation gas, not hydrogen gas.

A second aspect of the present invention relates to a fuel cell vehicleequipped with a fuel cell system. The fuel cell system includes a fuelcell that generates electric power through the reaction of a reactantgas, and a fluid compressor that compresses the reactant gas. The fluidcompressor may be any one of the fluid compressors described above.

According to the fuel cell vehicle of the present invention, because thefuel cell vehicle tends to be left in a low-temperature environment withtemperatures below 0° C. and tends to be in a situation where water mayenter the air compressor as a result of being driven in the rain or onthe snow. The upper passage, in communication with the inside of thepump chamber via the upper port, has advantage can be obtained due to astructure that at least a portion of the upper passage, which is incommunication with the inside of the pump chamber via the upper port, islocated below the upper port.

The fuel cell vehicle may further comprises a control unit that controlsthe fluid compressor to drive the rotor if it is determined that alow-temperature condition with a prescribed temperature or lower hascontinued for a specified period of time after the vehicle has shutdown. For example, the control unit rotates the rotor, for example, afew turns.

In fuel cell vehicle as described above, even if water is retained ingaps between the rotors or between the rotors due to surface tension andthe housing in the pump chamber and does not flow down after the vehicleis shut down, the rotation of the rotors causes the water to flow downand to be discharged out of the pump chamber easily.

The control unit may control the fluid compressor to rotatably drive therotor a plurality of times at regular time intervals if it is determinedthat the temperature of the surrounding environment has not exceeded athreshold temperature for a prescribed period of time after the vehiclehas been shut down.

According to the fluid compressor and the fuel cell vehicle of thepresent invention, excessive entry of water into the fluid compressorcan be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a basic configuration of a fuel cell vehicle according to afirst embodiment of the present invention;

FIG. 2 is a basic configuration of a fuel cell system that includes afluid control valve of the first embodiment;

FIG. 3 is a schematic cross-sectional view that illustrates an aircompressor shown in FIG. 2;

FIG. 4 is a cross-sectional view that is taken along the line A-A ofFIG. 3;

FIG. 5 is a partially simplified, enlarged view of the section B of FIG.3;

FIG. 6 is a view that corresponds to FIG. 5, which illustrates a secondexample of a suction duct portion;

FIG. 7 is a view that corresponds to FIG. 3 except that the rotor isomitted;

FIG. 8 is a perspective view that illustrates a twisted roots rotors asanother example of rotors;

FIG. 9 is a schematic cross-sectional view of an air compressoraccording to a second embodiment of the present invention;

FIG. 10 shows the basic configuration of a fuel cell system thatincludes a fluid control valve according to a third embodiment of thepresent invention;

FIG. 11 is a schematic cross-sectional view of the air compressor shownin FIG. 10; and

FIG. 12 is a flowchart that shows a method for controlling an aircompressor according to the third embodiment after the vehicle isshutdown.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 through FIG. 7 illustrate a first embodiment of the presentinvention. FIG. 1 shows the basic configuration of a fuel cell vehicleaccording to the first embodiment. As shown in FIG. 1, a fuel cellvehicle 10 is equipped with a fuel cell system 12. The fuel cell system12 includes a fuel cell stack (FC) 13 as a fuel cell. The fuel cellvehicle 10 includes the fuel cell stack 13 and a battery 14, provided atthe front of the vehicle, that serves as a secondary battery to storepower (left-hand side in FIG. 1). The fuel cell stack 13 is connected tothe battery 14 and the electric power generated by the fuel cell stack13 is supplied to the battery 14 to charge the battery 14. The battery14 and the fuel cell stack 13 are connected to two driving motors 16that serve as vehicle driving sources that are located at opposite sidesof the vehicle in the lateral direction thereof (the vertical directionof FIG. 1) via a booster converter or inverter (not shown) so thatelectric power from the battery 14 or the fuel cell stack 13 may besupplied to each driving motor 16. Each driving motor 16 includes arotating shaft and is respectively coupled to a corresponding wheel 18via a clutch mechanism (not shown) so that the wheels 18 are driven bythe driving motors 16. The fuel cell stack 13 may be indirectlyconnected to the driving motors 16 so that electric power from the fuelcell stack 13 is supplied to each of the driving motors 16 via thebattery 14.

It should be noted that the fuel cell vehicle 10 may instead have onlyone driving motor 16 and the driving motor 16 may be coupled to transmitpower with an axle (not shown) that drives the two wheels 18 via a powertransmission mechanism that includes a clutch mechanism. In this case,electric power may also be supplied only from the battery 14 to thedriving motor 16. The fuel cell vehicle according to the presentinvention is not restricted to this configuration, as long as the fuelcell vehicle is equipped with a fuel cell from which electric power canbe supplied to at least a driving motor or a power storage device. Afuel cell system that includes a fluid control valve (which is describedlater) is not restricted to use in a vehicle, and may be used in otherapplications.

The fuel cell system 12 will be described next. As shown in FIG. 2, thefuel cell system 12 includes the fuel cell stack 13; and a control unit20. The fuel cell stack 13 includes a plurality of unit fuel cellsstacked on top of each other, and current collecting plates and endplates at opposite ends of the fuel cell stack 13. The plurality of unitfuel cells, the current collecting plates and the end plates are clampedtogether with tie rods and nuts or the like. Insulating plates may beprovided between the current collecting plates and the end plates.

Although no detailed drawing of each unit fuel cell is given, each unitfuel cell includes, for example, a membrane assembly that is formed bysandwiching an electrolyte membrane between an anode and a cathode; andseparators that are disposed on each side of the membrane assembly. Ahydrogen-containing fuel gas may be supplied to the anode, and air maybe supplied to the cathode. Hydrogen ions that are generated by acatalytic reaction at the anode are transferred to the cathode throughthe electrolyte membrane, where the hydrogen ions undergo anelectrochemical reaction with oxygen to produce water. Also, electronsare transferred from the anode to the cathode through an externalcircuit to produce an electromotive force. That is, the fuel cell stack13 generates electric power through an electrochemical reaction betweenan oxidation gas and a fuel gas.

The fuel cell system 12 includes an oxidation gas supply passage 22through which air is supplied to the fuel cell stack 13; an oxidationgas-derived gas discharge passage 24 through which air off-gas that isthe air (oxidation gas) that has been used for the electrochemicalreaction on the cathode of the fuel cell stack 13, is discharged fromthe fuel cell stack 13; a fuel gas supply passage 26 through whichhydrogen gas is supplied to the fuel cell stack 13; a fuel gas-derivedgas discharge passage 28 through which hydrogen off-gas that is fuelgas-derived gas, i.e., the hydrogen gas which has been used for theelectrochemical reaction on the anode of the fuel cell stack 13, isdischarged from the fuel cell stack 13; and a fuel gas circulationpassage 30. An air inlet 32, an air cleaner 34 that removes foreignobjects from the air, and an air compressor 36 as a fluid control valveare located in an upstream portion of the oxidation gas supply passage22. The air pressurized by the air compressor 36 is humidified by ahumidifier 38 and then supplied to a cathode-side internal passage ofthe fuel cell stack 13. The air compressor 36 includes a pump 40; and amotor 42. The pump 40 is driven by driving the motor 42, and the drivingof the motor 42 is controlled by the control unit 20.

The air off-gas is discharged from the fuel cell stack 13 through theoxidation gas-derived gas discharge passage 24, and then is dischargedinto the atmosphere through a pressure control valve (not shown) afterit has been passed through the humidifier 38. The humidifier 38 alsodehumidifies the air off-gas and uses the obtained moisture to humidifythe air that is supplied to the fuel cell stack 13.

A fuel gas supply device, such as a high-pressure hydrogen tank (notshown) is located upstream of the fuel gas supply passage 26. Hydrogengas is supplied from the fuel gas supply device to the fuel cell stack13 via a fuel gas supply valve 44, which may be an electromagneticvalve.

The hydrogen off-gas, i.e., the hydrogen that has been used for theelectrochemical reaction, is discharged from the fuel cell stack 13through the fuel gas-derived gas discharge passage 28. The hydrogenoff-gas also contains unreacted hydrogen. The fuel gas circulationpassage 30 is provided to recirculate the hydrogen off-gas that isdischarged from the fuel cell stack 13 to the fuel gas supply passage 26and into the fuel cell stack 13.

A hydrogen pump 46 is provided in the fuel gas circulation passage 30.The hydrogen pump 46 returns the hydrogen off-gas to the fuel gas supplypassage 26 through the fuel gas circulation passage 30, and mixes thehydrogen off-gas with hydrogen gas that is supplied from the hydrogengas source to recirculate the hydrogen off-gas to the fuel cell stack13. The hydrogen pump 46 includes a pump 48, and a motor 50. The pump 48is driven by driving the motor 50, and the driving of the motor 50 iscontrolled by the control unit 20.

A gas-liquid separator 52 is provided at the connection between the fuelgas-derived gas discharge passage 28 and the fuel gas circulationpassage 30. A vent and drain passage 54 is connected to the gas-liquidseparator 52, and a purge valve 56, which may be an electromagneticvalve, is provided in the vent and drain passage 54. The hydrogenoff-gas, which is fed to the downstream side through the gas-liquidseparator 52 and the purge valve 56, are mixed with the air off-gassupplied through the oxidation gas-derived gas discharge passage 24 in adiluting device (not shown) to reduce the hydrogen concentrationsufficiently and then is discharged to the outside.

The air compressor 36, the hydrogen pump 46, the fuel gas supply valve44, and the purge valve 56 are connected to the control unit 20. Thecontrol unit 20, which is called ECU, outputs control signals to aninverter (not shown) that drives the motor 42 and 50 of the aircompressor 36 and the hydrogen pump 46, and outputs control signals tocontrol the opening and closing of the fuel gas supply valve 44 and thepurge valve 56.

A starter switch (not shown) that functions as an ignition switch forthe fuel cell system 12 is connected to the control unit 20. A powergeneration starting process is executed when a power generation startsignal, that is, a fuel cell activation command signal, is received fromthe starter switch, and a power generating operation stopping process isexecuted when a power generation stop signal is received. In otherwords, the control unit 20 controls power generation in the fuel cellstack 13. The control unit 20 includes a microcomputer that has a CPU,memory and so on.

A bypass passage 58 is provided between the oxidation gas supply passage22 and the oxidation gas-derived gas discharge passage 24. The bypasspassage 58 redirects and discharges air that is fed from the upstreamside of the oxidation gas supply passage 22 through the oxidationgas-derived gas discharge passage 24, not through the fuel cell stack13. An upstream three-way valve 60 is provided at the connection betweenthe oxidation gas supply passage 22 and the bypass passage 58, and adownstream three-way valve 62 is provided at the connection between theoxidation gas-derived gas, discharge passage 24 and the bypass passage58. Each of the three-way valves 60 and 62 is connected to the controlunit 20, and the control unit 20 may change the direction of flowthrough each three-way valves 60 and 62 based on the pressure of the airthat is supplied to the fuel cell stack 13 or the like. The upstreamthree-way valve 60 may selectively direct the air fed through theoxidation gas supply passage 22 to either the fuel cell stack 13 or thebypass passage 58. The downstream three-way valve 62 selectively directsthe air fed from the upstream side of the bypass passage 58 to flowdownstream or shuts off the flow. As for the triangles that represent athree-way valve in the drawings, a white triangle indicates that thechannel is open, and a black triangle indicates that the channel isclosed. Therefore, in the configuration that is shown in FIG. 2, no airis fed to the bypass passage 58. Each of the three-way valves 60 and 62is used to control the pressure of air that is supplied to the fuel cellstack 13. The humidifier 38 may be omitted.

Referring next to FIG. 3 through FIG. 8, the configuration of the aircompressor 36 that serves as the fluid control valve will be describedin detail. As shown in FIG. 3, the air compressor 36 is a volumecompression, screw type compressor with a body that is inclined withrespect to the y-direction, i.e., vertical direction. In the aircompressor 36, the motor 42 is coupled to the lower end of the pump 40via a timing gear 64. The pump 40 has a housing 68 that defines thereina pump chamber 66; a suction duct 72, serving as an upper connectionmember, that is secured to the upper surface of a top plate 70, whichserves as a wall portion of the housing 68; and a delivery duct portion76, which serves as a lower connection member, that is secured to thelower end of a side wall portion 74 of the housing 68 that extendsobliquely downward. In other words, the suction duct portion 72 and thedelivery duct portion 76 are secured to upper and lower portions,respectively, of the housing 68. A driving rotor 78 and a driven rotor(not shown) are rotatably supported parallel to each other in thehousing 68. The driving rotor 78 has a driving shaft that has a threadedportion 80 formed on its outer peripheral surface. The driving shaft iscoupled to the rotating shaft of the motor 42, and is rotated by drivingthe rotating shaft. The driven rotor has a driven shaft that has athreaded portion formed on its outer peripheral surface as with thedriving rotor 78. The timing gear 64 has a gear housing 82 that includestherein two timing gears (not shown). The two timing gears are securedto the lower ends of the driving shaft and the driven shaft,respectively, and are in mesh with each other. The driving shaft and thedriven shaft therefore rotate synchronously. The rotating shaft of themotor 42 is coupled to a lower end portion of the driving shaft thatextends downward from one of the timing gears. The driving shaft and thedriven shaft are inclined with respect to the y-direction and thex-direction, i.e., horizontal direction.

A suction port 84, that is an upper port which extends through the topplate portion 70 at the upper end of the housing 68 in the thicknessdirection thereof, is formed. As shown in FIG. 4, the suction port 84has a generally C-shaped axial cross-section so as to avoid the rotationsupport portions (not shown) at the upper ends of the driving shaft anddriven shaft. As shown in FIG. 3, the suction duct 72 defines therein asuction passage 86, which serves as an upstream passage, with a firstend (left end in FIG. 3) that opens in an end face of the suction ductportion 72 and a second end (right end in FIG. 3) that communicates withthe suction port 84. One end of a separate pipe (not shown) may bebolted to the end face (left end face in FIG. 3) of the suction ductportion 72. Accordingly, bolt holes may be provided at the end face ofthe suction duct portion 72 to receive mounting bolts.

At the lower end of a side wall portion 74 facing the delivery ductportion 76, a delivery port 88, which serves as a lower port, is formedthrough the side wall portion 74. The delivery duct portion 76 definestherein a delivery passage 90 with a first end (left end in FIG. 3) thatopens in an end face of the delivery duct portion 76 and a second end(right end in FIG. 3) in communication with an end of the delivery port88. One end of another separate pipe (not shown) may be bolted to theend face (left end face in FIG. 3) of the delivery duct portion 76. Forexample, boltholes may be formed in the end face of the delivery ductportion 76 for receiving mounting bolts. Each of the duct portions 72and 76 may be provided with a flange, in which boltholes are formed, atthe pipe-connecting end of the respective duct portions 72 and 76.

When the rotors 78 rotate, the closed spaces that are defined by thethread grooves between the individual turns of the thread portions ofthe rotors 78 and the inner surface of the housing 68 move from thesuction side to the delivery side in the pump chamber 66, and, whilecompressing the air that is introduced into the pump chamber 66 throughthe suction duct portion 72, discharges the compressed air to theoutside through the delivery duct portion 76. In this case, the suctionpassage 86 directs air that is introduced from the upstream side of thepipe connected to the suction duct portion 72 into the pump chamber 66through the suction port 84. The delivery passage 90 delivers air thathas been compressed in the pump chamber 66 to the pipe (not shown)connected to the delivery duct 76.

As shown in detail in FIG. 5, the suction passage side end, i.e., thelower end P1 of the upstream end, of the suction port 84 is locatedbelow the pump chamber 66 side end, i.e., the lower end P2 of thedownstream end, of the suction port 84. Also, the lower edge L1 of thesuction passage 86 along the flow direction is inclined in such a manneras to slope downwardly gradually from the suction port 84 side to thepipe connecting side. In other words, in a cross-section of the suctionpassage 86 that is taken along the flow direction, the lower edge L1along the flow direction is inclined downwardly. In addition, at least apart of the suction passage 86 is located below the suction port 84.More specifically, the lower edge L1 of the suction passage 86 extendsdownward from the lower edge L1A of the suction port 84. The uppermostportion of the bottom of the suction passage 86 is connected to thelower end P1, i.e., the lowermost portion of the suction passage 86 sideend, of the suction port 84.

As shown in FIG. 3, a bottom surface 92 (lower end face in FIG. 3) ofthe pump chamber 66 is a flat surface that extends generallyperpendicular to the axial direction of the rotors 78, and the loweredges of the delivery port 88 and the delivery passage 90 along the flowdirection are located in a phantom plane that includes the bottomsurface 92. The lower edges of the delivery port 88 and the deliverypassage 90 are located on a straight line perpendicular to the axis ofthe rotors 78. The delivery port 88 includes a portion that coincideswith the lowermost end a of the inner surface of the pump chamber 66,and extends downward directly from the bottom surface 92 of the pumpchamber 66. Therefore, the bottom surface 92 of the pump chamber 66 andthe lower edges of the delivery port 88 and the delivery passage 90 areflush with each other. Also, the lower edge L2 of the delivery passage90 slopes downward gradually from the delivery port 88 to the pipeconnecting side. In other words, in a cross-section of the deliverypassage 90 that is taken along the flow direction, the lower edge L2along the flow direction is inclined downward. In addition, at least apart of the delivery passage 90 is located below the delivery port 88.

The lower edges of the suction passage 86 and the delivery passage 90may also be curved. For example, FIG. 6 is a view that illustrates asecond example of the suction port 84 and the suction duct portion 72.The lower edge L1A of the suction port 84 may extend parallel to theaxial direction of one of the rotors such as the driving rotor 78 (seeFIG. 3), and the suction passage 86 side end of the suction port 84 islocated above the pump chamber 66 side end of the suction port 84.Namely, the lower end P1A of the upstream end of the suction port 84 islocated above the lower end P2A of the downstream end of the suctionport 84. Also, the lower edge L1 of the suction passage 86 along theflow direction slopes downward gradually from the suction port 84 sideto the pipe connecting side. In other words, in a cross-section of thesuction passage 86 taken along the flow direction, the lower edge L1along the flow direction curves downward in an upwardly convex manner.It should be noted, however, that the entirety of the lower edge L1 ofthe suction passage 86 is not necessarily located below the suction port84, and the entirety of the lower edge L2 of the delivery passage 90(FIG. 3) is not necessarily located below the delivery port 88 (FIG. 3).

In the case of either the air compressor 36 that is shown in FIG. 3 andFIG. 5 or the second example of the air compressor 36 that is shown inFIG. 6, excessive entry of water into the air compressor 36 can beprevented. In this regard, the water entry prevention function of theair compressor 36 shown in FIG. 3 and FIG. 5 is described with referenceto FIG. 7. In FIG. 7, the white arrows Q1 and Q2 indicate the directionin which air flows into the air compressor 36 and the direction in whichair flows out of the air compressor 36, respectively. Also, the arrows Rindicate the direction in which water flows. The arrows S indicate thedirection in which water flows down on the driving rotor 78 (see FIG. 3)in the pump chamber 66. Because at least a part of the suction passage86 is located below the suction port 84 and the lower edge L1 of thesuction passage 86 is located below the lower edge L1A of the suctionport 84 as shown in FIG. 7, the water that has accumulated on the wallsurface of the suction passage 86 flows to the pipe connecting side(leftward in FIG. 7) as indicated by the arrows R, thereby preventingthe entry of an excessive amount of water into the pump chamber 66. Inaddition, even if water has entered the pump chamber 66 or if water hascondensed in the pump chamber 66, the water flows on the bottom surface92 in the pump chamber 66 and is easily discharged to the outsidethrough the delivery port 88 and the delivery passage 90.

Because at least a part of the suction passage 86 in communication withthe inside of the pump chamber 66 through the suction port 84 is locatedbelow the suction port 84 as described above, even if water, such ascondensate water, has accumulated on the wall surface of the suctionpassage 86, the water may be easily discharged to the outside and entryof excessive water into the pump chamber 66 from the suction port 84side can be prevented. Therefore, formation of ice from the water thathas entered the pump chamber 66 and failures caused by the formation ofice in the pump chamber 66, such as inability to restart the aircompressor 36 smoothly, are less likely to occur.

In addition, the pump chamber 66 is defined within the housing 68 and,the suction port 84 and the delivery port 88 are formed through the topplate portion 70 and the side wall portion 74, respectively, each ofwhich forms a part of the housing 68. The suction passage 86 is definedwith in the suction duct portion 72, which is secured to an upperportion of the housing 68 and to which a pipe is connectable. Thedelivery duct portion 76, to which a pipe is connectable, is secured toa lower portion of the housing 68, and the delivery passage 90 isdefined within the delivery duct portion 76. Therefore, in aconfiguration in which the housing 68, the suction duct portion 72, andthe delivery duct portion 76 are separate components, failures caused byformation of ice in the pump chamber 66 are less likely to occur. Thefluid compressor is not limited to one that has a housing and separatesuction duct portion and delivery duct portion, and the suction ductportion and the delivery duct portion may be integrated with a housingthat defines therein a pump chamber. In this case, each duct portionprotrudes outward from a wall portion that forms part of the housing,and each port is formed through a wall portion and has a length equal tothe thickness of the wall portion.

In addition, because the bottom portion of the suction passage 86 isinclined or curved to slope downwardly gradually from the suction port84 to the pipe connecting side of the suction passage 86, water that hasaccumulated on the wall surface of the suction passage 86 may bedischarged to the outside more effectively.

In the configuration shown in FIG. 5 and FIG. 7, because the lower endP1 (the suction passage 86 side end) of the suction port 84 is locatedbelow the lower end P2 (the pump chamber 66 side end) of the suctionport 84, water that has accumulated on the wall surface of the suctionport 84 can be discharged to the outside more effectively.

In addition, because at least a portion of the delivery passage 90 islocated below the delivery port 88, even if water has accumulated on thewall surface of the delivery passage 90, the water may be easilydischarged to the outside and entry of an excessive amount of water intothe pump chamber 66 from the delivery port 88 side may be prevented. Inother words, even if the delivery passage 90 is located below the pumpchamber 66, as in this embodiment, water that has been discharged fromthe pump chamber 66 is prevented from flowing back into the pump chamber66. Therefore, failures caused by formation of ice in the pump chamber66 are much less likely to occur.

The delivery port 88 includes the lower edge a (FIG. 3), which islocated on the bottom surface 92, and extends downward directly from thebottom surface 92 of the pump chamber 66, without any difference inlevel. Therefore, even if water has entered or condensed in the pumpchamber 66, the water may be easily discharged and prevented fromremaining in the pump chamber 66 more effectively and failures caused byformation of ice in the pump chamber 66 are much less likely to occur.

Because each of the driving rotor 78 and the driven rotor has a threadedportion, i.e., a spiral ridge, even if water is present on the rotors78, the water easily flows down along the thread, which makes water lesslikely to remain on the rotors 78 after the air compressor 36 is stoppedwhen because the vehicle is shut down.

In addition, because the air compressor 36 is used to compress air, thesuction passage 86 has advantage that can be obtained by a structurethat a portion of the suction passage 86 is located below the suctionport 84.

The fuel cell vehicle of this embodiment, which is equipped with thefuel cell system 12 that includes the air compressor 36 as describedabove, tends to be left in a low-temperature environment withtemperatures below 0° C. and tends to be in a situation where water mayenter the air compressor 36 as a result of being driven in the rain oron the snow. Therefore, the bottom of the suction passage 86 incommunication with the inside of the pump chamber 66 via the suctionport 84 has an advantage which can be obtained by a structure that aportion of the suction passage 86 is located below the suction port 84.

In the above example, a case in which each of the driving rotor 78 andthe driven rotor are threaded and the air compressor 36 is a volumecompression, screw type compressor has been described. However, thepresent invention is not restricted to this configuration. For example,the driving rotor 78 and the driven rotor may be twisted roots rotors.FIG. 8 illustrates twisted roots rotors as a second example of therotors that are included in the air compressor. A driving rotor 94 and adriven rotor 96 that are disposed in the air compressor 36 have aplurality of spiral lobes 98 which are twisted in the same directionwith respect to the axial direction. The embodiment that has beendescribed above is applicable to a volume compression, twisted rootstype air compressor that uses the rotors 94 and 96.

FIG. 9 illustrates an air compressor according to a second embodiment ofthe present invention. In the second embodiment, the suction port 84 islocated at a lower portion of the housing 68, and the delivery port 88is located at an upper portion of the housing 68. The suction ductportion 72, which defines therein a suction passage 86, is secured to alower portion of the housing 68, and the delivery duct portion 76, whichdefines therein a delivery passage 90, is secured to an upper portion ofthe housing 68.

That is, with the first embodiment, the air compressor 36 is a volumeCompression, screw type compressor with a body that is inclined withrespect to the y-direction, i.e., vertical direction. In the aircompressor 36, the motor 42 is coupled to the upper end of the pump 40via the timing gear 64. The delivery duct portion 76 serves as an upperconnection member of the pump 40 and is secured to the upper end of anupper side wall portion 74A of the housing 68, and the suction ductportion 72 serves as a lower connection member of the pump 40 that issecured to the lower surface of a bottom plate portion 100 of thehousing 68. The driving rotor 78 (see FIG. 3) and the driven rotor, eachof which has a threaded portion that is formed thereon, are disposed inthe housing 68.

The delivery port 88, which is an upper port that extends through theupper side wall portion 74A of the housing 68 in the thickness directionthereof, is formed at the upper end of the upper side wall portion 74A.The delivery duct portion 76 defines therein a delivery passage 90 as anupstream passage that has a first end (right end in FIG. 9) which opensin an end face of the delivery duct portion 76 and a second end (leftend in FIG. 9) in communication with an end of the delivery port 88.

The suction port 84, which is a lower port that extends through thebottom plate portion 100, which faces the suction duct portion 72 of thehousing 68 in the thickness direction thereof, is formed. The suctionduct portion 72 defines therein the suction passage 86 as a downstreampassage that has a first end (right end in FIG. 9), which opens in anend face of the suction duct portion 72, and a second end (left end inFIG. 9) in communication with an end of the suction port 84.

The end of the lower edge of the delivery port 88 near the deliverypassage 90 in communication with the inside of the pump chamber 66 viathe delivery port 88 is lower than the lower edge of the delivery port88 near the pump chamber 66. The lower edge of the delivery passage 90along the flow direction slopes downward gradually from the deliveryport 88 side to the pipe connecting side (left side in the drawing). Inother words, in a cross-section of the delivery passage 90 taken alongthe flow direction, the lower edge along the flow direction is inclineddownwardly. In addition, at least a portion of the delivery passage 90is located below the delivery port 88.

The suction port 84 includes a portion that coincides with the lowermostend β of the inner surface of the pump chamber 66, and extends downwarddirectly from the inner surface of a side wall surface 102 of the pumpchamber 66. Also, the lower edge of the suction passage 86 is curved toslope downward gradually from the suction port 84 side to the pipeconnecting side. In addition, at least a portion of the suction passage86 is located below the suction port 84.

In the embodiment as described above, because at least a portion of thedelivery passage 90 is located below the delivery port 88, even if waterhas accumulated on the wall surface of the delivery passage 90, thewater may be easily discharged to the outside and excessive entry ofwater from the delivery port 88 side into the pump chamber 66 isprevented. In this case, water that has accumulated on the wall surfacesof the delivery port 88 and the delivery passage 90 flows down to thepipe connecting side as indicated by the arrows R and is discharged tothe outside easily. In addition, the water that has accumulated on thewall surfaces of the suction port 84 and the suction passage 86 alsoflows down to the pipe connecting side as indicated by the arrows R andis discharged to the outside easily. Therefore, formation of ice andfailures caused by the ice made from water that has entered the pumpchamber 66, such as inability to restart the air compressor 36 smoothly,are less likely to occur. The other configuration and effects are thesame as those of the first embodiment except that the positionalrelationships between the delivery port 88 and the delivery passage 90,and the suction port 84 and the suction passage 86 in the verticaldirection are opposite. Also in this embodiment, the rotors are notlimited to threaded rotos and may be of another type such as a twistedroots type.

FIG. 10 through FIG. 12 illustrate a third embodiment of the presentinvention. In the fuel cell system 12 that constitutes a fuel cellvehicle 10 (see FIG. 1) of this embodiment, an inverter 104 connected toa motor 42 that drives a pump 40 of an air compressor 36 so that ACcurrent, converted from DC current provided from the battery 106, may besupplied to the motor 42 as shown in FIG. 10. The inverter 104 isconnected to a control unit (ECU) 20, and the ECU 20 outputs controlsignals to the inverter 104. With this configuration, the ECU 20controls the motor 42 via the inverter 104. The ECU 20 and the inverter104 constitute an inverter control unit (ICU) 108. A temperature sensorTa is provided in air inlet 32 to detect the temperature of air flowingthrough the air inlet 32. A second temperature sensor Tb is providedbetween an air cleaner 34 and the air compressor 36 in an oxidation gassupply passage 22 to detect the temperature of air flowing through theoxidation gas supply passage 22. A temperature sensor, which is attachedto an air flow meter provided to detect the flow rate in this section,may be used as the second temperature sensor Tb. The temperaturesdetected by the temperature sensor Ta and the second temperature sensorTb are input into the control unit 20.

The air compressor 36 is constituted as shown in FIG. 11. In particular,the air compressor 36 is a screw type compressor in which a drivingrotor 78 (see FIG. 3) and a driven rotor (not shown), each of which hasa threaded portion, are rotatably disposed with the axial direction ofthe rotors 78 extending vertically. The entire air compressor 36 isdisposed along a vertical direction. In the air compressor 36, a motor42 is coupled to the upper end of a pump 40 via a timing gear 64. Thepump 40 has a suction duct portion 114 that protrudes from and isintegrated with the upper end of a side wall portion 110 that forms oneside (left side in FIG. 11) of a housing 68, and a delivery duct portion116 that protrudes from and integrated with the lower surface of abottom plate portion 112 of the housing 68.

A suction port 84 as an upper port that extends through the side wallportion 110 in the thickness direction thereof is formed at the upperend of the side wall portion 110. The suction duct 114 defines therein asuction passage 86, which serves as an upper passage. The suction duct114 and the suction passage 86 are inclined with respect to the verticaldirection with at least a portion of the suction passage 86 locatedbelow the suction port 84. The lower edges of the suction port 84 andthe suction passage 86 are inclined with respect to the verticaldirection.

The delivery port 88, which extends through the housing 68 in thethickness direction thereof, is formed through a portion of the bottomplate portion 112 that faces the delivery duct portion 116 of thehousing 68. The delivery duct portion 116 and a delivery passage 90defined therein generally extend vertically, and the pipe-connecting endof the delivery passage 90 faces downward. In this case, the bottomplate portion 112 is almost located on a horizontal phantom plane. Inthe air compressor 36, entry of an excessive amount of water into thepump chamber 66 may be prevented by properly defining the positionalrelationship between the suction port 84 and the suction passage 86.However, if there is a recess that is concave downward or the like inthe bottom plate portion 112 of the housing 68 as shown in FIG. 11, apuddle 118 may be formed on the bottom plate portion 112 as shown inFIG. 11 if water enters the pump chamber 66 or water is formed bycondensation in the pump chamber 66. With such a configuration, watermay freeze if the air compressor 36 is left in a low temperatureenvironment with a temperature below 0° C. The air compressor 36 may bealso left in a low-temperature environment with water retained in thesmall gaps between the two rotors (not shown) or between the rotors andthe inner surface of the housing 68 by surface tension. In this case,the water present in the gaps may freeze. The air compressor 36 has roomfor improvement in terms of the improvement of the starting performancewhen left in a low-temperature environment. This embodiment overcomesthe problem.

In the fuel cell vehicle 10 of this embodiment (see FIG. 1), the controlunit 20 controls the air compressor 36 to drive the driving rotor 78(see FIG. 3) and the driven rotor to rotate, for example, a few turns ifit is determined that the temperature has remained equal to or below athreshold temperature for a prescribed period of time after the vehicleis shut down.

FIG. 12 is a flowchart that shows the method for controlling the aircompressor 36 after the vehicle is shutdown. First, in step S12, if thecontrol unit 20 determines that the fuel cell system 12 is shut down by,for example, detecting turn-off of the starter switch in step S10, thecontrol unit 20 activates at least one of the temperature sensor Ta andthe second temperature sensor Tb to detect the temperature at presettime intervals and stores the detected temperatures. That is, thecontrol unit 20 starts temperature monitoring using the temperaturesensor Ta (or Tb).

Then, in step S14, the control unit 20 determines whether the detectedtemperature has remained equal to or below a threshold temperature, forexample, 0° C. or lower, for a prescribed period of time. If it isdetermined the detected temperature has been equal to or lower than thethreshold temperature for at least the prescribed period of time, theprocess goes to step S16. In step S16, the control unit 20 determineswhether the air compressor 36 has been already forcibly rotated afterthe shutdown of the vehicle. If it is determined that the air compressor36 has been already forcibly rotated, the process proceeds to step 18,where the control unit 20 drives the motor 42 of the air compressor 36to forcibly rotate each rotor of the air compressor 36 a few turns.

In contrast, if the control unit 20 determines in step S14 that thedetected temperature has not been equal to or below a thresholdtemperature for at least the prescribed period of time, or determines instep S16 that the air compressor 36 has been already forcibly rotatedafter the shutdown of the vehicle, the operation of the control unit 20is terminated.

In this embodiment as described above, even if water is retained in gapsbetween the two rotors or between the rotors and the housing 68 of thepump chamber 66 by surface tension and does not flow down after shutdownof the vehicle, the rotation of the rotors causes the retained water toflow down and to be discharged out of the pump chamber 66 easily. Thatis, even a few turns of the rotors may be sufficient to cause the waterretained in the gaps to flow down. In addition, the water that hasaccumulated on the bottom may be easily discharged through the deliveryport 88 by through the rotation of the rotors. It should be noted thatthe control unit 20 may rotatably drive the rotors at a prescribedrotational speed for a specified period of time after the vehicle isshut down in order to use the centrifugal force more effectively.

In addition, because the air compressor 36 is not forcibly rotated againif the air compressor 36 has already been forcibly rotated aftershutdown of the vehicle, excessive consumption of the battery 106 may beprevented. However, the determination in step S16 may be omitted and theforcible rotation of the air compressor 36 may be carried out severaltimes if the control unit 20 determines that the electrical charge inthe battery 106 is at least equal to a predetermined value. The controlunit 20 may drive the rotors at regular time intervals so that therotors rotate preset plural times each time the control unit 20 drivesthe rotors if the temperature has remained equal to or below a thresholdtemperature for at least a prescribed period of time. In the case ofthese configurations, the water in the air compressor 36 may bedischarged to the outside more easily after the vehicle is shut down.

While both temperature sensor Ta and the second temperature sensor Tbare provided in this embodiment, a single temperature sensor may beprovided and the detection signals from the single temperature sensormay be input into the control unit 20. Because the other configurationand effects are the same as those of the first embodiment that is shownin FIG. 1 to FIG. 8, similar components are designated by the samereference numerals to omit redundant illustration and description.

While an air compressor 36 with two rotors, the driving rotor 78 and thedriven rotor, has been described in each of the above embodiments, thefluid compressor of the present invention may also be applied to an aircompressor that has a single rotor. For example, the present inventionis applicable to the configuration of a scroll type fluid compressor inwhich a single spiral rotor is disposed in a housing that includestherein a spiral wall portion.

While the present invention has been described in the context of an aircompressor in each of the above embodiments, the present invention isnot restricted to such a configuration and is also applicable to, forexample, the hydrogen pump 46 (see FIG. 2), which pressurizes anddelivers hydrogen off-gas.

1. A fuel cell system, comprising: a fuel cell that generates electricpower through a reaction of a reactant gas, and a fluid compressor,wherein the fluid compressor includes: a pump chamber defined within ahousing; an upper port that is provided at an upper portion of the pumpchamber and a lower port that is provided at a lower portion of the pumpchamber, wherein the upper port and the lower port are formed through awall of the housing; an upper passage that is in communication with theinside of the pump chamber via the upper port and serves as a suctionpassage that directs a fluid into the pump chamber through the upperport; wherein an upper connection member, to which a pipe is connectedis secured to an upper portion of the housing and the upper passage isdefined within the upper connection member, and wherein the upperpassage has a lower edge that is inclined or curved gradually downwardfrom the upper port to a pipe connecting end of the upper passage; alower passage that is in communication with the inside of the pumpchamber via the lower port and serves as a delivery passage thatdelivers the fluid from the pump chamber through the lower port, whereina lower connection member, to which another pipe is connected, issecured to a lower portion of the housing and the lower passage isdefined within the lower connection member; and a rotor that is providedin the pump chamber and that rotates to compress a fluid introduced intothe pump chamber through the upper port and then discharge thecompressed fluid through the lower port, wherein at least a part of theupper passage is positioned below the upper port, and at least a portionof an upper passage side end of the upper port is located below a pumpchamber side end of the upper port, and wherein the fluid compressor isused as an air compressor that compresses oxidation gas as the reactantgases which is supplied to the fuel cell.
 2. A fuel cell system,comprising: a fuel cell that generates electric power through a reactionof a reactant gas, and a fluid compressor, wherein the fluid compressorincludes: a pump chamber defined within the housing; an upper port thatis provided at an upper portion of the pump chamber and a lower portthat is provided at a lower portion of the pump chamber, wherein theupper port and the lower port are formed through a wall of the housing;an upper passage that is in communication with the inside of the pumpchamber via the upper port and serves as a delivery passage thatdelivers a fluid from the pump chamber through the upper port, whereinan upper connection member, to which a pipe is connected, is secured toan upper portion of the housing and the upper passage is defined withinthe upper connection member, and wherein the upper passage has a loweredge that is inclined or curved gradually downward from the upper portto a pipe connecting end of the upper passage; a lower passage that isin communication with the inside of the pump chamber via the lower portand serves as a suction passage that directs the fluid into the pumpchamber through the lower port, wherein the lower connection member, towhich another pipe is connected, is secured to a lower portion of thehousing and the lower passage is defined within the lower connectionmember; and a rotor that is provided in the pump chamber and thatrotates to compress the fluid introduced into the pump chamber throughthe lower port and then discharges the compressed fluid through theupper port, wherein at least a part of the upper passage is positionedbelow the upper port and at least a portion of an upper passage side endof the upper port is located below a pump chamber side end of the upperport, and wherein the fluid compressor is used as an air compressor thatcompresses oxidation gas as the reactant gases which are supplied to thefuel cell.
 3. (canceled)
 4. (canceled)
 5. The fuel cell system accordingto claim 1, wherein at least a portion of the lower passage ispositioned below the lower port.
 6. The fuel cell system according toclaim 5, wherein the lower port includes a portion that is a lowermostend of an inner surface of the pump chamber, and extends downward from abottom surface of the pump chamber or a side wall surface that includesthe lowermost end.
 7. (canceled)
 8. (canceled)
 9. The fuel cell systemaccording to claim 1, wherein the rotor has a spiral ridge.
 10. The fuelcell system according to claim 1, wherein an uppermost portion of abottom of the upper passage is connected to a lowermost portion of theupper passage side end of the upper port.
 11. The fuel cell systemaccording to claim 10, wherein the uppermost portion of the bottom ofthe upper passage is connected to the lowermost portion of the bottom ofthe upper port.
 12. A fuel cell vehicle equipped with a fuel cell systemaccording to claim
 1. 13. The fuel cell vehicle according to claim 12,further comprising: a control unit that controls the fluid compressor torotatably drive the rotor if it is determined that an environmentaltemperature does not exceed a threshold temperature for a prescribedperiod of time after the fuel cell vehicle is shut down.
 14. The fuelcell vehicle according to claim 13, wherein the rotor is driven aplurality of times at regular time intervals if the control unitdetermines that the environmental temperature does not exceed thethreshold temperature for a prescribed period of time after the fuelcell vehicle is shut down.
 15. (canceled)
 16. (canceled)
 17. The fuelcell system according to claim 2, wherein at least a portion of thelower passage is positioned below the lower port.
 18. The fuel cellsystem-according to claim 17, wherein the lower port includes a portionthat is a lowermost end of an inner surface of the pump chamber, andextends downward from a bottom surface of the pump chamber or a sidewall surface that includes the lowermost end.
 19. The fuel cell systemaccording to claim 2, wherein the rotor has a spiral ridge.
 20. The fuelcell system according to claim 2, wherein an uppermost portion of abottom of the upper passage is connected to a lowermost portion of theupper passage side end of the upper port.
 21. The fuel cell systemaccording to claim 20, wherein an uppermost portion of a bottom of theupper passage is connected to a lowermost portion of the upper passageside end of the upper port.
 22. A fuel cell vehicle equipped with a fuelcell system according to claim
 2. 23. The fuel cell vehicle according toclaim 22, further comprising: a control unit that controls the fluidcompressor to rotatably drive the rotor if it is determined that anenvironmental temperature does not exceed a threshold temperature for aprescribed period of time after the fuel cell vehicle is shut down. 24.The fuel cell vehicle according to claim 23, wherein the rotor is drivena plurality of times at regular time intervals if the control unitdetermines that the environmental temperature does not exceed thethreshold temperature for a prescribed period of time after the fuelcell vehicle is shut down.